Interpretive Summary: No-till has changed crop production in the Great Plains; one change has been some producers are diversifying their rotations. This diversity in crops has enabled producers to develop a population-based approach to weed management, consequently reducing the need for herbicides. A further benefit of crop diversity is that some crops can improve the following crop’s tolerance to weeds. For example, winter wheat is 3 times more tolerant of wild rye interference when following dry pea compared to soybean as a preceding crop. Preceding crop also affect weed tolerance of corn and soybean. In some way, synergism among crops improves tolerance to weed interference. Integrating no-till with diverse crop rotations has enabled producers in the semiarid steppe of the U.S. to manage weeds with 50% less cost compared to tilled rotations with less crop diversity. A further benefit is that crop tolerance to weed interference can be increased.

Technical Abstract:
Cropping systems in the Great Plains of the United States are changing because of no-till. Rotations now include a diversity of crops in contrast with rotations in tilled systems that grow only one or two crops. This change in rotation design has enabled producers to develop population-based weed management, which has reduced cost of weed management 50%. A further benefit of crop diversity is that crop tolerance to weeds may be improved by the preceding crop. Some crops, such as dry pea and corn, improve water-use-efficiency of following crops; these crops also improve crop tolerance to weed interference. For example, corn tolerance to foxtail millet interference was more than two-fold higher following dry pea compared with either soybean or spring wheat as preceding crops. A similar level of synergy occurred when dry pea preceded winter wheat and corn preceded soybean. In some way, these crops synergize the following crop to improve tolerance to weed interference. The cause of crop synergy is likely related to a multitude of interacting factors such as growth-promoting substances, microbial changes, and nutrient cycling. No-till rotations that include a diversity of crops are synergistically improving land productivity and resource-use-efficiency in the Great Plains. A further benefit is that crop tolerance to weed interference can be increased.